<!DOCTYPE HTML>
<html>
<head>
<style>
#target5 {
        position: absolute;
        top: 0px;
        left: 0px;
        width: 20px;
        height: 20px;
        background: #f00;
}
</style>
<body>
<div id="target5"></div>
<script>
        var io = new IntersectionObserver(function (records) {
                window.parent.postMessage(records[0].rootBounds == null, 'http://mochi.test:8888');
        }, {});
        io.observe(document.getElementById("target5"));
</script>
</body>
</html>
